System and method thereof for dynamically adjusting sleep/awake intervals of wireless network device

ABSTRACT

A system and a method thereof for dynamically adjusting sleep/awake intervals of a wireless network device are provided. The system has at least one base station (BS) and at least one wireless network device. The system performs the method to dynamically adjust the sleep/awake intervals by properly delaying and combining delivery of data such that the wireless network device is turned into a sleep mode after finishing data delivery within an adjusted period. Thereby, the number of awake frames of a mobile subscriber station (MSS) can be reduced without sacrificing the quality of service (QoS).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 97119934, filed on May 29, 2008. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a system and a method thereoffor a wireless communication device, and more particularly, to a systemand a method thereof for dynamically adjusting the sleep/awake intervalsof a wireless network device to reduce the power consumption.

2. Description of Related Art

The Worldwide Interoperability for Microwave Access (WiMAX) is a newwireless broadband network system, and the system adopts the 802.16standard established by the Institute of Electrical and ElectronicsEngineers, Inc. (IEEE) as its operation standard. The IEEE 802.16estandard was further established in 2005 to meet the requirements ofmobile wireless communications. The IEEE 802.16e standard is wellfocused in broadband wireless access (BWA) techniques due to itscharacteristics such as broad bandwidth, high portability, greatcoverage, and good connection quality, etc.

In the IEEE 802.16e standard, the connection between a base station (BS)and a mobile subscriber station (MSS) is accomplished through thetransmission/reception of a series of frames. To achieve higherefficiency in wireless communication applications, different quality ofservice (QoS) types are defined in the IEEE 802.16e standard regardingdifferent network environments, such as Unsolicited Grant Service (UGS),real-time Polling Service (rtPS), Extended rtPS (ErtPS), non-real-timePolling Service (nrtPS), and Best Effort (BE) service.

How to prolong the operation time of an IEEE 802.16e MSS by reducing thepower consumption thereof is a very important subject. Threepower-saving modes are defined in the IEEE 802.16e standard in order toreduce the power consumption. FIG. 1 is a timing diagram of the IEEE802.16e standard in the three power-saving modes. Referring to FIG. 1,the sleep time 20 and listen time 22 of a MSS in three differentpower-saving modes 14, 16, and 18 when the MSS is within a sleep stateperiod 12 are illustrated., wherein the sleep state period 12 is betweentwo normal operation periods 10. The MSS is in a normal operation modeduring the normal operation periods 10, while the MSS is in a sleep modeduring the sleep state period 12. Foregoing three power-saving modes 14,16, and 18 are started when the MSS is in the sleep mode.

In the first power-saving mode 14, the MSS wakes up in the listen time22 after sleeping for some time to listen whether there is any packet tobe received. If there is no packet to be received, the next sleep time20 of the MSS is extended exponentially. This power-saving mode issuitable for the data transmission of BE and nrtPS.

In the second power-saving mode 16, the MSS also wakes up after sleepingfor some time to listen whether there is any packet to be received. Ifthere is no packet to be received, the MSS enters the sleep mode again.The difference of this power-saving mode from the first power-savingmode is that the sleep time 20 in the second power-saving mode has afixed length. Accordingly, the second power-saving mode is suitable fortransmitting real-time data, such as the data transmission of UGS andrtPS.

In the third power-saving mode 18, the BS specifies the sleep time 20,and the MSS returns to the normal operation mode after a sleep time 20.

In the 802.16e standard, a MSS can establish multiple connections at thesame time, and each of the connections has its own sleep time and listentime. The time a MSS can actually sleep and listen has to lbe calculatedif the MSS has multiple connections. As shown in FIG. 2, the MSS A hasthree connections and each of the connections has its own sleep time 24and listen time 26. Thus, the MSS A can only enter the sleep mode whenall the three connections thereof are in sleep state (i.e., the period28 in FIG. 2), and this is very inefficient in terms of the powerconsumption of the MSS.

Regarding the power-saving mechanism of the IEEE 802.16e standard, mostexisting patents are focused on sensor networks and wireless local areanetworks (WLAN). As to the academic field, even though the power-savingmechanism specified by the IEEE 802.16e standard has been studied, theacademic documents are mostly focused on performance analysis withmathematical models, and wherein only real-time data types, but notthose non-real-time data types which are mostly transmitted over thenetworks, are considered.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method fordynamically adjusting the sleep/awake intervals of a wireless networkdevice, wherein the performance of the power-saving mechanism specifiedin the IEEE 802.16e standard is improved and accordingly the powerconsumption is reduced.

The present invention provides a method for dynamically adjusting thesleep/awake intervals of a wireless network device. An exemplary exampleof the method includes: determining at least one awake frame candidateset of the wireless network device according to the transmission cycleand the maximum grant delay of at least one periodic conmection of thewireless network device; determining at least one sleep interval and atleast one awake interval of the wireless network device according to thedata generation rate and the maximum grant delay of at least onenon-periodic connection of the wireless network device; and determiningan actual sleep interval and an actual awake interval of the wirelessnetwork device according to the awake frame candidate set, the sleepinterval, and the awake interval.

The present invention provides a system for dynamically adjusting thesleep/awake intervals of a wireless network device. An exemplary exampleof the system includes at least one wireless network device and at leastone base station (BS). A plurality of connections are establishedbetween the BS and the wireless network device, and the BS determines atleast one awake frame candidate set of the wireless network deviceaccording to the transmission cycle and the maximum grant delay of atleast one periodic connection among these connections. The BS determinesat least one sleep interval and at least one awake interval of thewireless network device according to the data generation rate and themaximum grant delay of at least one non-periodic connection among theseconnections. After that, the BS determines an actual sleep interval andan actual awake interval of the wireless network device according to theawake frame candidate set, the sleep interval, and the awake interval.

The present invention provides a method for dynamically adjusting thesleep/awake intervals of a wireless network device. An exemplary exampleof the method includes: determining a grant delay range of each relayingframe of a plurality of periodic connections of the wireless networkdevice according to the transmission cycles and the maximum grant delaysof the periodic connections; and then determining an awake framecandidate set of the wireless network device according to theoverlapping of the grant delay range of each relaying frame, andallowing the wireless network device to transmit data within therelaying frames in the awake frame candidate set.

The present invention provides a method for dynamically adjusting thesleep/awake intervals of a wireless network device. An exemplary exampleof the method, a minimum value of the maximum grant delays of aplurality of non-periodic connections of the wireless network device isobtained according to the information of the maximum grant delays of thenon-periodic comnections. Besides, in the method, a queue size isobtained according to the length of the i^(th) sleep interval, thelength of the i^(th) awake interval, and the data generation rates ofthe non-periodic connections of the wireless network device, wherein iis a positive integer. After that, the length of the (i+1)^(th) awakeinterval of the wireless network device is obtained according to thequeue size and a link capacity of the wireless network device. Moreover,the length of the (i+1)^(th) sleep interval of the wireless networkdevice is obtained according to the minimum value, the length of thei^(th) sleep interval, the length of the i^(th) awake interval, and thelength of the (i+1)^(th) awake interval, and the total length of thei^(th) sleep interval, the i^(th) awake interval, the (i+1)^(th) sleepinterval, and the (i+1)^(th) awake interval is restricted to be lessthan or equal to the minimum value. The wireless network device iscontrolled to be in the sleep mode during the i^(th) sleep interval andthe (i+1)^(th) sleep interval and transmit data during the i^(th) awakeinterval and the (i+1)^(th) awake interval.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a timing diagram of the IEEE 802.16e standard in threepower-saving modes.

FIG. 2 is a timing diagram of three connections of a mobile subscriberstation (MSS) A.

FIG. 3 is a timing diagram of three Unsolicited Grant Service (UGS)connections of a MSS B.

FIG. 4 illustrates several possibilities of combining the awake framesof two UGS connections according to the exemplary embodiment consistentof the present invention.

FIG. 5 illustrates a method for combining the awake frames of three UGSconnections according to the exemplary embodiment consistent of thepresent invention.

FIG. 6 is a timing diagram of an awake interval and a sleep interval ofa real-time Polling Service (rtPS), an Extended rtPS (EitPS), or anon-real-time Polling Service (nrtPS) connection according to theexemplary embodiment consistent of the present invention.

FIG. 7 is another timing diagram of an awake interval and a sleepinterval according to the exemplary embodiment consistent of the presentinvention.

FIG. 8 illustrates a first situation of determining an actual awakeinterval according to the exemplary embodiment consistent of the presentinvention.

FIG. 9 illustrates a second situation of determining an actual awakeinterval according to the present invention.

FIG. 10 illustrates a third situation of determining an actual awakeinterval according to the exemplary embodiment consistent of the presentinvention.

FIG. 11 illustrates a fourth situation of determining an actual awakeinterval according to the exemplary embodiment consistent of the presentinvention.

FIG. 12 is a functional block diagram of a system for dynamicallyadjusting the sleep/awake intervals of a wireless network deviceaccording to the exemplary embodiment consistent of the presentinvention.

FIG. 13 shows the comparison between the power consumption in theconventional technique and the power consumption according to theexemplary embodiment consistent of the present invention.

FIG. 14 shows the comparison between the downlink delay in theconventional technique and the downlink delay according to the exemplaryembodiment consistent of the present invention.

FIG. 15 shows the comparison between the uplink delay in theconventional technique and the uplink delay according to the exemplaryembodiment consistent of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

The present invention provides a mechanism for extending the sleep timeof a mobile subscriber station (MSS), and accordingly reducing the powerconsumption thereof, without losing the quality of service (QoS) inregard to both real-time and non-real-time data types. Exemplaryembodiments consistent of the present invention, a power-savingmechanism for dynamically adjusting the sleep time of a MSS is providedbased on the operation concept that the lengths of the sleep/awakeintervals are non-periodic and whether the MSS is in the sleep state orthe listen state is determined by the traffic load and the QoSrequirement of the third power-saving mode in the IEEE 802.16e standard.

FIG. 3 illustrates a method for dynamically adjusting the sleep/awakeintervals of a periodic connection of a wireless network device.Referring to FIG. 3, the MSS B has three Unsolicited Grant Service (UGS)comnections UGS1, UGS2, and UGS3, the data characteristics of each UGSconnection are indicated by a transmission cycle (p) and a maximum.grant delay (gd), and an awake frame candidate set of the MSS B isobtained. In the present example, the transmission cycle p of the firstconnection UGS1 is 4, and the maximum grant delay gd thereof is 1; thetransmission cycle p of the second connection UGS2 is 5, and the maximumgrant delay gd thereof is 2; and the transmission cycle p of the thirdconnection UGS3 is 4, and the maximum grant delay gd thereof is 2.During a frame 1, the first comnection UGS1 has a packet to transmit;however, because the maximum grant delay gd thereof is 1, the MSS Blooks into the next frame 2. Then, since the third comnection UGS3 alsohas a packet to transmit during the frame 2, the MSS B delays the packetof the first comnection UGS1 for a frame and wakes up during the frame 2to transmit the packets of both the first connection UGS1 and the thirdconnection UGS3. Similarly, during the frame 3, the second comnectionUGS2 has a packet to transmit, and since the maximum grant delay gdthereof is 2, the MSS B looks into the next frame. Then since the firstconnection UGS1 also has a packet to transmit during the frame 5, theMSS B stays in the sleep state until the frame 5 and then wakes up totransmit the packets of both the first connection UGS1 and the secondcomnection UGS2. Through the method described above, non-periodicsleep/awake intervals can be calculated, and the sleep time of the MSScan be prolonged without sacrificing the QoS. Other than the real-timeUGS data type, in the present invention, the sleep/awake intervals whenthe MSS transmits non-real-time data types, such as non-real-timePolling Service (nrtPS) and Best Effort (BE), may also be calculatedwithout sacrificing the QoS. As described above, because both real-timeand non-real-time data transmissions in the IEEE 802.16e standard areconsidered in the dynamic power-saving mechanism of a MSS provided bythe present invention, the requirements of different channel settingscan be met.

The exemplary embodiment consistent of the present invention provides amethod for dynamically adjusting the sleep/awake intervals regarding amobile WiMAX (i.e. IEEE 802.16e) network so as to reduce the powerconsumption. The major difference of the present invention from theconventional techniques is that the method provided by the presentinvention supports the definition in the WiMAX standard. Since real-timePolling Service (rtPS) and Extended rtPS (ErtPS) have the same trafficparameters, the rtPS will be described below as an example.Additionally, in order to achieve the best power-saving effect, BE datais transmitted together in the awake intervals. In order to achieveforegoing purpose, the power-saving method in the present invention hasthree procedures, and these procedures will be respectively describedbelow.

First Procedure: Determining an Awake Frame Candidate Set of a PeriodicConnection

A periodic UGS connection is taken as an example in this procedure. Inorder to transmit the packets of each UGS connection within the sameframe, the UGS data frames distributed at different time points have tobe combined together according to the transmission cycle, the dataquantity, and the maximum grant delay of the UGS connections, and inwhich frame these data frames are combined has to be determined.

More than one possible awake frame intervals are obtained by executingthe first procedure, and an awake frame interval may include a pluralityof continuous frames or only one frame. Even though only a possibleawake frame interval is obtained, during the actual operation, one ofthe frames is simply selected from the possible awake frame interval fortransmitting data. This is because when a plurality of MSSs switchbetween the sleep and awake modes, a MSS in the awake mode will use thebandwidth originally assigned to a MSS in the sleep mode; similarly,when the MSS enters the sleep mode, the resources in the sleep intervalthereof can be released and used by a MSS which switches from the sleepmode to the awake mode. In an embodiment of the present invention, theawake frame candidate set is calculated through matrix algebra, whereinthe number of awake frames is determined according to the actuallyaccumulated data quantity. In addition, since the execution result ofthe first procedure is at least one “possible” awake frame interval, theat least one “possible” awake frame interval can be referred as an“awake frame candidate set”.

FIG. 4 illustrates the design concept of the first procedure. The firstframe of the first connection UGS1 and the 3^(rd) frame of the secondconnection UGS2 may also be combined into the 4^(th) frame or the 5^(th)frame besides being combined into the 3^(rd) frame provided that thedelayed time of each delayed frame does lot exceed the maximum grantdelay of the corresponding UGS connection.

To be more specific, in the first procedure, the next frame in which theMSS is to be waken up for transmitting data is first located regardingeach UGS connection before the data is combined, the nearest frame isthen located according to the maximum grant delay of the UGS connection,and besides, which frames can be combined with this frame is furtherdetermined. As shown in FIG. 5, the MSS has three UGS connections UGS1,UGS2, and UGS3. Taking the connection UGS1 as an example, thetransmission cycle p thereof is 5 (i.e., the cornection UGS1 transmitsdata during the 2^(nd), the 7^(th), the 12^(th) . . . frame), and themaximum grant delay gd thereof is 3 (i.e., the data to be transmitted inthe 2^(nd) frame can be delayed at most to the 5^(th) frame). The firstrelaying frames of the three UGS connections are respectively the2^(nd), the 3^(rd), and the 6^(th) frame. With the maximum grant delaysof the three connections UGS1, UGS2, and UGS3 being respectively 3, 2,and 4, an grant delay range of each relaying frame can be determined.Namely, it can be determined that the connections UGS1, UGS2, and UGS3can respectively transmit data within the frame periods [2, 3, 4, 5],[3, 4, 5], and [6, 7, 8, 9, 10]. Thus, the awake frame candidate set canbe determined according to the overlapping of the grant delay range ofeach relaying frame. For example, the data of the connections UGS1 andUGS2 can be combined and transmitted during the frame period [3, 4, 5],and the second relaying frames of the connections UGS1 and UGS2 can becombined with the first relaying frame of the connection UGS3 into theframe period [7, 8]. Accordingly, the two awake frame candidate sets arerespectively determined as the frame period [3, 4, 5] and the frameperiod [7, 8].

Foregoing algorithm can be expressed with following pseudo codes:

-   -   step 1: Let [F_(i,j), Y_(i,j)] be the next awake-frame candidate        set of connection (i,j), where F_(i,j) is the next transmission        frame of comnection (i, j), and Y_(i,j)=F_(i,j)+d(i, j). We        define [F_(i,j), Y_(i,j)]<[F_(i,k), Y_(i,k)] if        F_(i,j)<F_(i,k,s) or F_(i,j)=F_(i,k) and Y_(i,j)<Y_(i,k,) where        j≠k. Let S be the union of the next awake-frame candidate sets        of all UGS connections.    -   step 2: Choosing the smallest [F_(i,s), Y_(i,s)] in S. Let        F=F_(i,s), Y=Y_(i,s). Update S by S=S−[F_(i,s), Y_(i,s)].    -   step 3: If S is empty, go to step 6. Else go to step 4.    -   step 4: Choosing the smallest [F_(i,j), Y_(i,j)] in S. If        F_(i,j)≦Y, go to step 5. Else go to step 6.    -   step 5: Let F=max[F_(i,j), F], Y=min[Y_(i,j), Y]. Update S by        S=S−[F_(i,j), Y_(i,j)]. Go to step 3.    -   step 6: Get the next awake-frame candidate set [F, Y].

In foregoing pseudo codes, (i,j) represents the j^(th) connection of thei^(th) MSS, d(i, j) represents the maximum grant delay of the connection(i, j). [F_(i,j), Y_(i,j)] represents the next awake flame candidate setof the connection (i, j), F_(i,j) represents a first frame in the awakeframe candidate set [F_(i,j), Y_(i,j)] of the connection (i, j), Y_(i,j)represents a last frame in the awake frame candidate set [F_(i,j),Y_(i,j)] of the connection (i, j), and S represents a union set of thenext awake frame candidate sets of all the connections. In step 1 andstep 2, the relative sizes of the awake frame candidate sets of all theUGS connections are determined, a smallest candidate set (i.e., thecandidate set [F_(i,s), Y_(i,s)]) is selected and assigned as the nextawake-frame candidate set [F, Y], and the candidate set [F_(i,s),Y_(i,s)] is removed from the union set S. The relative sizes of theawake frame candidate sets are first determined according to thesequence of the first frames thereof on the time axis, and an awakeframe candidate set having an earlier first frame is considered smallerthan an awake frame candidate set having a later first frame. In short,if F_(i,j)<F_(i,k), then [F_(i,j), Y_(i,j)]<[F_(i,k), Y_(i,k)]; however,if the first frames of two awake frame candidate sets are located at thesame position on the time axis, the relative sizes of these two awakeframe candidate sets are further determined according to their lastframes. In short, if F_(i,j)=F_(i,k) and Y_(i,j)<Y_(i,k), then [F_(i,j),Y_(i,j)]<[F_(i,k), Y_(i,k)]. The reason for determining the awake-framecandidate set [F, Y] is that a connection having a smaller awake framecandidate set needs to wake up earlier for transmitting data thereforeshould have higher priority. Besides, because the smallest candidate set[F_(i,s), Y_(i,s)] or [F_(i,j), Y_(i,j)] has been deleted from the unionset S in step 2 or step 5, the union set S in step 3 includes the awakeframe candidate sets of other connections; however, if the union set Sis empty, there is no more awake frame candidate set of any otherconnection in the union set S, and accordingly the awake-frame candidateset [F, Y] is the awake frame candidate set of the UGS connection of theMSS. In step 4, which awake frame candidate set can be combined with thecurrent awake-frame candidate set [F, Y] is sequentially located in theunion set S. If the sets can be combined, step 5 is executed to updatethe values of F and Y, and the updated value of F is the maximum valuebetween the original value of F and the current value of F_(i,j), andthe updated value of Y is the minimum value between the original valueof Y and the current value of S_(i,j). Contrarily, if there is no moreawake frame candidate set to be combined or there is no awake framecandidate set of any other connection in the union set S, the awakeframe candidate set regarding each connection is updated in step 6.Referring to FIG. 5, in step 1, the first awake frame of the connectionUGS1 is the frame 2 (i.e., F_(i,j)=2), and since the maximum grant delaythereof is 3, the last frame in the first awake frame candidate setthereof is 2+3=5, and accordingly [2, 3, 4, 5] is the first awake framecandidate set thereof. Since the connection UGS1 is a periodicconnection, the subsequent awake frame candidate sets thereof can besequentially obtained. Similarly, the first awake frame candidate setsof the connections UGS2 and UGS3 are respectively [3, 4, 5] and [6, 7,8, 9, 10]. It can be understood by comparing the three awake framecandidate sets that [2, 3, 4, 5]>[3, 4, 5]>[6, 7, 8, 9, 10]. In step 2,the smallest awake frame candidate set is [2, 3, 4, 5], and accordinglyF=2 and Y=5. In step 4, the current smallest awake frame candidate setis [3, 4, 5], and accordingly F_(i,j)=3 and Y_(i,j)=5. Since(F_(i,j)=3)≦(Y=5) the procedure proceeds to step 5. In step 5, F=max[3,2]=3, )=min[5, 5]=5, and accordingly the first awake frame candidate setcombined and transmitted by the connections UGS1 and UGS2 is [3, 4, 5].In step 6, the second awake frame candidate set of the connection UGS2is further combined. This is because the second awake frame candidateset of the connection UGS1 is [7, 8, 9, 10], the second awake framecandidate set of the connection UGS2 is [6, 7, 8], the first awake framecandidate set of the connection UGS3 is [6, 7, 8, 9, 10], andaccordingly the smallest set among foregoing three sets is [6, 7, 8]based on foregoing definition.

In exemplary embodiments consistent of the present invention, an awakeframe candidate set is determined according to the transmission cyclesand the maximum grant delays of a plurality of periodic connections of awireless network device. The step for determining the awake framecandidate set includes determining a grant delay range of each relayingframe according to the maximum grant delay of each connection anddetermining the awake frame candidate set according to the overlappingof the grant delay range of each relaying frame.

Second Procedure: Calculating an Awake Interval and a Sleep Interval ofa Non-Periodic Connection (a rtPS, an ErtPS, or an nrtPS Connection)

The system accumulates the data for some time and then transmits theaccumulated data together regarding a rtPS, an ErtPS, or a lrtPSnon-periodic connection, wherein the frames for transmitting the dataare referred as awake intervals, and those frames not for transmittingdata are referred as sleep intervals. The data transmitted within eachawake interval is the data accumulated in a previous awake interval anda previous sleep interval. Refering to FIG. 6, S_(i) and W_(i)respectively represent the i^(th) sleep interval and the i^(th) awakeinterval of a MSS A, and d(A,k) represents the maximum grant delay of aconnection k of the MSS A. Before entering the sleep mode, the MSS Ainforms the BS about its queue size, and the BS assigns the bandwidthduring the awake intervals of the MSS A to allow the MSS A to transmitdata. Thus, the data to be transmitted during the (i+1)^(th) awakeinterval (i.e., the awake interval W_(i+1)) of the MSS A is accumulatedduring the sleep interval S_(i) and the awake interval W_(i), and thedata to be transmitted during the (i+2)^(th) awake interval (i.e., theawake interval W_(i+2)) is accumulated during the sleep interval S_(i+1)and the awake interval W_(i+1).

The second procedure is to determine the number of frames in an awakeinterval and a sleep interval. As shownl in FIG. 6, the MSS informs theBS about the data quantity generated during the frame period 1˜8 beforethe 8^(th) frame is over and transmits the data during the frame period12˜14. In order to ensure the QoS during the delayed time, it is assumedthat the packet enters the queue at the begimning of the frame 1 (i.e.,the time point T₁) and is only transmitted before the frame 14 is over(i.e., at the time point T₂), so that the total length of the intervalsS_(i+1), W_(i+1), S_(i+2), and W_(i+2) cannot be greater than themaximum grant delay d(A,k). In addition, if only a small quantity ofdata is accumulated in the intervals S_(i+1) and W_(i+1), the awakeinterval W_(i+2) is correspondingly shorter so that the sleep intervalS_(i+2) can be longer. However, if a large quantity of data isaccumulated during the sleep interval S_(i+2) due to the long sleepinterval S_(i+2), a long awake interval W_(i+3) is required to transmitthe data packet, and which may cause the total length of the intervalsS_(i+2), W_(i+2), S_(i+3) , and W_(i+3) to be longer than the maximumgrant delay d(A,k). As a result, the requirement to the QoS cannot bemet. In this case, the sleep interval S_(i+3) can be adjusted (even to0), and in order to avoid the situation that the QoS cannot be met, thetotal length of the intervals S_(i+2), W_(i+2), and W_(i+3) has to beless than or equal to the maximum grant delay d(A,k). It should be notedthat the sleep interval S_(i+3) is 0 when the total length of theintervals S_(i+2), W_(i+2), and W_(i+3) is equal to the maximuin grantdelay d(A,k). As described above, the awake interval and the sleepinterval can be obtained thlrough following expressions (1) and (2):

$\begin{matrix}\{ \begin{matrix}{{S_{i + 1} + W_{i + 1} + S_{i + 2} + W_{i + 2}} \leq {d( {A,k} )}} \\{{S_{i + 2} + W_{i + 2} + W_{i + 3}} \leq {d( {A,k} )}}\end{matrix}  & (1) \\{W_{i + 1} = \lbrack \frac{\sum\limits_{j}{{\lambda ( {A,j} )}( {S_{i} + W_{i}} )}}{\sum\limits_{j}{\mu_{\min}( {A,j} )}} \rbrack} & (2)\end{matrix}$

λ(A,j) in foregoing expression (2) represents the data quantitygenerated in each frame by the connection j of the MSS A, andμ_(min)(A,j) represents the minimum data quantity which can betransmitted by the connection j of the MSS A within each frame. When thesleep interval S_(i) and the awake interval W_(i) are already obtained,the awake interval W_(i+1) can be obtained through foregoing expression(2), and the sleep interval S_(i+1) can be obtained through foregoingexpression (1).

How to determine the lengths of the awake interval and the sleepinterval will be described herein with reference to FIG. 7. Here it isassumed that the queue of a MSS is empty when the MSS is about to enterthe sleep mode, and the numbers of frames in the first sleep interval S₁and the first awake interval W₁ are both 1. Besides, it is assumed thata frame is 1 second, the MSS has six coiuieccions, and the datageneration rates of the six connections are respectively 256 Kbps, 256Kbps, 512 Kbps, 512 Kbps, 2 Mbps, and 2 Mbps. If the maximum grantdelays d(A,k) of the six connections are respectivly 4, 4, 5, 5, 6, and6 frames, the smallest maximum grant delay d(A,4k) is then 4. Moreover,it is assumed that the lilk capacity of the MSS is 20 Mbps, namely, theMSS can transmit 20 Mbits data within a frame time. Thus, the dataquantity accumulated in the first sleep interval S₁ and the first awakeinterval W₁ is (256 Kbits×2+512 Kbits×2+2Mbits ×2)×2=11.072 Mbits data.The second awake interval (i.e. the awake interval W₂) needs only oneframe to transmit the 11.072 Mbits data. In consideration that thesmallest maximum grant delay d(A,k) has to be equal to 4, the secondsleep interval S₂ can have at most one (i.e., 4−1−1−1) frame. In orderto avoid such a situation that too much data is accumulated during thesecond sleep interval S₂ and the second awake interval W₂ due to thelong second sleep interval S₂ and accordingly the data cannot becompletely transmitted within the maximum delay time even when the framenumber in the sleep interval S₃ is 0, whether S₂+W₂+W₃ is smaller thanor equal to 4 has to be further verified. Since the data accumulatedduring the interval S₂ and the interval W₂ are both 11.072 Mbits, theframe number in the third awake interval W₃ can be obtained as 1.Accordingly, the total length of the intervals S₂, W₂, and W₃ is equalto 3 (i.e., 1+1+1). Thus, the condition that (S₂+W₂+W₃) has to besmaller than or equal to the smallest maximum grant delay d(A,k) is met.In other words, if the two packets respectively enter the queue at thetime points T_(in1) and T_(in2) and are respectively sent out at thetime points T_(out1) and T_(out2), the time durations (T_(out1)−T_(in1))and (T_(out2)−T_(in2)) are both shorter than or equal to the smallestmaximum grant delay d(A,k).

Through the method described above, in the second procedure, the maximumvalue S_(max) of each sleep interval is obtained without sacrificing theQoS, so that the awake time of the MSS is relatively shortened, and themaximum value S_(max) is defined as the maximum sleep interval S_(max).

In embodiments of the present invention, the step for determining thesleep interval and the awake interval includes obtaining the minimumvalue of the maximum grant delays of a plurality of non-periodicconnections and restricting the lengths of the sleep interval and theawake interval according to the minimum value. The actual sleep intervaland the actual awake interval are determined according to the relativeposition of a last frame in the awake frame candidate set to the sleepinterval and the awake interval on the time axis.

Third Procedure: The BS Determining the Actual Awake Interval and theActual Sleep Interval of the MSS According to the Awake Frame CandidateSet, the Awake Interval, and the Sleep Interval

In the third procedure, the results obtained in the first procedure andthe second procedure are integrated to determine an actual awakeinterval and an actual sleep interval of a MSS. As described above, inthe first procedure, the data of a UGS connection is combined to obtainthe awake frame candidate set [F, Y], and in the second procedure, themaximum sleep interval S_(max) and the awake interval W are obtainedaccording to the data of the rtPS connection, the ErtPS connection, orthe nrtPS connection. In the third procedure, the results obtained inthe first procedure and the second procedure are integrated to obtainthe actual awake interval and the actual sleep interval of the MSS. Tobe specific, the actual sleep interval and the actual awake interval aredetermined according to the relative position of a last frame Y in theawake frame candidate set [F, Y] to the maximum sleep interval S_(max)and the awake interval W on the time axis. How to determine the actualawake interval and the actual sleep interval of the MSS in the thirdprocedure regarding three different situations will be described belowwith reference to FIGS. 8˜11:

-   (1) there are only UGS connections: the next frame in which the MSS    wakes up is the last frame in the candidate set. As shown in FIG. 8,    the MSS wakes up during the Y^(th) frame and the Y^(th) frame.-   (2) there are only rtPS, ErtPS, or nrtPS connections: assuming the    frame before the maximum sleep interval S_(max) is the N^(th) frame,    then the next frame in which the MSS wakes up is the frame    [N+S_(max)+1˜N+S_(max)+W]. As shown in FIG. 9, the actual awake    interval is the interval 50.-   (3) there is at least one of the rtPS, ErtPS, and nrtPS connections    and there are UGS connections: the present embodiment focuses on the    combination result of UGS data, if there is an awake frame candidate    set of the UGS coiu-ection in the interval S_(max), the MSS sleeps    until the (Y−1)^(th) frame, and the awake interval W is brought    forward to start from the Y^(th) frame. Thus, the actual awake    interval is the frame [Y˜Y+W−1]. As shown in FIG. 10, the actual    awake interval is the interval 52, and the first awake frame is the    Y^(th) frame. However, if the awake frame candidate set [F,Y] of the    UGS connection overlaps the awake interval W, the awake interval is    the frame [S_(max)+1˜S_(max)+W], namely, the actual awake interval    is the frame of the awake interval W. As shown in FIG. 11, the    actual awake interval is the interval 54.

The algorithm in the third procedure can be expressed with followingpseudo codes:

-   -   step 1: Let X be the set of all awake-frarne candidate sets step        2: Find the candidate set with the smallest F value from X, and        denoted as [F₁, Y₁]. step 3: For [F₁, Y₁], finding the closest        sleep and awake intervals and denoting them as [S, W]. The first        frame in S is represented as s₁. The number of frames in W is        represented as Num_(w).step 4: If Y₁<s₁, adding a new awake        frame that is equal to Y₁ then go to step 7; else go to step 5.        step 5: If Y₁∩S≠0, adjusting awake interval W to be [Y₁,        Y₁+Num_(w)−1] then go to step 7; else go to step 6; step 6: If        Y₁∩W≠0, awake interval W remains intact. Go to step 7.    -   step 7: X=X−[F, Y], and go to step 2.

In short, the awake interval and sleep interval [S, W] of a rtPS, anErtPS, or an nrtPS connection closest to the awake frame candidate set[F, Y] of each UGS connection are first obtained, and then whether theawake frame candidate set [F, Y] intersects the [S, W] is determined tocombine the data. In step 4, whether the awake frame candidate set [F,Y] intersects the [S, W] is first determined. If there is nointersection between the two, an awake interval (i.e., the interval Y)is added to the awake frame candidate set [F, Y]. In step 5, whether theawake frame candidate set [F, Y] intersects the union set S is furtherdetermined. If there is intersection between the two, the entire awakeinterval W is brought forward. In step 6, whether the awake framecandidate set [F, Y] intersects the awake interval W is furtherdetermined. If there is intersection between the two, the entire awakeinterval W is unchanged. Finally, the currently determined awake framecandidate set [F, Y] is removed from all the awake frame candidate sets.and then the procedure returns to step 2 to determine the next awakeframe candidate set.

Because the power consumed by the wireless network device during theactual sleep interval is lower than the power consumed by the sameduring the actual awake interval, the actual awake interval of thewireless network device can be greatly shortened through the methoddescribed above and accordingly the power consumption thereof can beconsiderably reduced.

FIG. 12 is a functional block diagram of a system 100 for dynamicallyadjusting the sleep/awake intervals of a wireless network device.Referring to FIG. 12, the system 100 includes at least one BS 102 and awireless network device 104. In the IEEE 802.16e standard, the wirelessnetwork device 104 is a MSS. A plurality of connections 106 isestablished between the BS 102 and the MSS 104 fortransmitting/receivinig frames, wherein each of the connections 106 maybe a UGS, an rtPS, an ErtPS, an nrtPS, or a BE comnection. The BS 102dynamically adjusts the sleep/awake intervals of the MSS 104 through thethree procedures described above so as to reduce the power consumptionof the MSS 104.

The method for dynamically adjusting the sleep/awake intervals of thewireless network device will be discussed respectively from the MSS endand the BS end:

-   -   (1) The MSS end: the MSS 104 needs only send a message to the BS        102 through piggyback before the current awake interval thereof        is over to notify the BS 102 that it is going to enter a sleep        interval and what its current queue size is. The major advantage        of this mechanism is that no additional hardware is to be added        to the existing MSS 104 and no new frame format is to be        defined.    -   (2) The BS end: after receiving the queue size from the MSS 104,        the BS 102 calculates the sleep time of the MSS 104 and the        resources (i.e., the number of frames) to be assigned to the MSS        104 when next time it wakes up according to the QoS parameters        of each connection 106 of the MSS 104, so as to determine the        actual sleep interval and the actual awake interval of the MSS        104. Because the actual sleep interval and the actual awake        interval can be notified to the MSS 104 through downlink-MAP        (DL-MAP) and uplink-MAP (UL-MAP), the BS 102 does not need not        to define a new frame format. The MSS 104 can switch between the        sleep mode and the awake mode according to the actual sleep        interval and the actual awake interval defined by the BS 102.

FIGS. 13-15 are diagrams illustrating the performance estimation of themethod for dynamically adjusting the sleep/awake intervals of a wirelessnetwork device through program simulations. First, the power consumptionrate is defined as the quotient obtained by dividing the number of awakeframes by the number of all the frames. As shown in FIG. 13, compared tothe power-saving mechanism defined in the IEEE 802.16e standard, themethod in the present invention greatly reduces the number of awakeframes at a node. In addition, FIGS. 14 and 15 respectively show thecomparison result of the delay time performance regarding a downlinkconnection and an uplink connection between the present invention andthe conventional art. Because the method in the present inventionreduces the power consumption by delaying data transmission, the averagedelay time is longer than that in the IEEE 802.16e standard; however,the method in the present invention still meets the requirement of aconnection to the maximum delay time.

It should be noted that even though foregoing embodiments are describedbased on the IEEE 802.16e network structure, the present invention isnot limited thereto. Any technique which conforms to the concept of“respectively calculating the awake frame candidate set and the maximumsleep interval according to real-time and non-real-time data types andthen dynamically adjusting the sleep/awake intervals according to theawake frame candidate set and the maximum sleep interval” is within thescope of the present invention.

In overview, the exemplary embodiment consistent of the presentinvention provides a power-saving mechanism for dynamically adjustingthe sleep/awake intervals of a wireless network, especially of an IEEE802.16e Mobile WiMAX network, wherein a MSS is allowed to enter a sleepmode after transmitting data within an interval by appropriatelydelaying and combining the data to be transmitted. In the presentinvention, the number of awake frames is greatly reduced at the MSS end,but user's requirements to the QoS (including the operation bandwidthand the average delay time etc) is still met.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A method for dynamically adjusting sleep/awake interals of a wirelessnetwork device, the method comprising: determining at least one awakeframe candidate set of the wireless network device according to atransmission cycle and a maximum grant delay of at least one periodicconnection of the wireless network device; determining at least onesleep interval and at least one awake interval of the wireless networkdevice according to a data generation rate and a maximum grant delay ofat least one non-periodic connection of the wireless network device; anddetermining an actual sleep interval and an actual awake interval of thewireless network device according to the awake frame candidate set, thesleep interval, and the awake interval.
 2. The method as claimed inclaim 1, wherein the periodic connection is an Unsolicited Grant Service(UGS) connection.
 3. The method as claimed in claim 1, wherein thenon-periodic connection is selected from a group consisted of areal-time Polling Service (rtPS) connection, an Extended rtPS (ErtPS)connection, and a non-real-time Polling Service (nrtPS) connection. 4.The method as claimed in claim 1, wherein the awake frame candidate setis determined according to transmission cycles and maximum grant delaysof a plurality of periodic connections of the wireless network device.5. The method as claimed in claim 4, wherein the step for determiningthe awake frame candidate set comprises: delaying data transmission ofeach of the connections according to the maximum grant delay of theconnection, and restricting the delayed time of the data transmission tobe less than or equal to the maximum grant delay of the comnection. 6.The method as claimed in claim 4, wherein the step for determining theawake frame candidate set comprises: determnimng a grant delay range ofa relaying frame according to the maximum grant delay of each of theconnections; and determining the awake frame candidate set according tooverlapping of the grant delay range of each of the relaying frames. 7.The method as claimed in claim 1, wherein the sleep interval and theawake interval are determined according to data generation rates andmaximum grant delays of a plurality of non-periodic connections of thewireless network device.
 8. The method as claimed in claim 7, whereinthe step for determining the sleep interval and the awake intervalcomprises: obtaining a minimum value of the maximum grant delays of thenon-periodic connections; and restricting a length of the sleep intervaland a length of the awake interval according to the minimum value. 9.The method as claimed in claim 7, wherein the step for determining thesleep interval and the awake interval comprises: calculating a relayeddata quantity according to the data generation rates of the non-periodicconmections and the lengths of a previous sleep interval, a previousawake interval, and the sleep interval; and calculating the length ofthe awake interval according to the relayed data quantity and a linkcapacity of the wireless network device.
 10. The method as claimed inclaim 9, wherein the step for determining the sleep interval and theawake interval comprises: adjusting the length of the sleep intervalaccording to the relayed data quantity.
 11. The method as claimed inclaim 1, wherein the actual sleep interval and the actual awake intervalare determined according to a relative position of a last frame in theawake frame candidate set to the sleep interval and the awake intervalon a time axis.
 12. The method as claimed in claim 11, wherein the stepfor determining the actual sleep interval and the actual awake intervalcomprises: setting the last frame in the awake frame candidate set as apart of the actual awake interval when the last frame in the awake framecandidate set overlaps neither the sleep interval nor the awakeinterval.
 13. The method as claimed in claim 11, wherein the step fordetermining the actual sleep interval and the actual awake intervalcomprises: bringing the awake interval forward when the last frame inthe awake frame candidate set overlaps the sleep interval.
 14. Themethod as claimed in claim 11, wherein the step for determining theactual sleep interval and the actual awake interval comprises: settingthe actual awake interval as the awake interval when the last frame inthe awake frame candidate set overlaps the awake interval.
 15. Themethod as claimed in claim 1, wherein the wireless network deviceestablishes connections and relays data according to IEEE 802.16estandard.
 16. A system for dynamically adjusting sleep/awake intervalsof a wireless network device, comprising: at least one wireless networkdevice; and at least one base station (BS), wherein a plurality ofconnections is established between the BS and the wireless networkdevice, the BS determines an awake frame candidate set of the wirelessnetwork device according to a transmission cycle and a maximum grantdelay of a periodic connection among the connections, the BS alsodetermines a sleep interval and an awake interval of the wirelessnetwork device according to a data generation rate and a maximum grantdelay of a non-periodic connection among the connections, and the BSfurther determines an actual sleep interval and an actual awake intervalof the wireless network device according to the awake frame candidateset, the sleep interval, and the awake interval.
 17. The system asclaimed in claim 16, wherein the periodic connection is an UnsolicitedGrant Service (UGS) connection.
 18. The system as claimed in 16, whereinthe non-periodic connection is selected from a group consisted of anrtPS comnection, an ErtPS connection, and an nrtPS connection.
 19. Thesystem as claimed in claim 16, wherein the colnections are establishedaccording to IEEE 802.16e standard.
 20. A method for dynamicallyadjusting the sleep/awake intervals of a wireless network device,comprising: determining a grant delay range of each relaying frame of aplurality of periodic connections of the wireless network deviceaccording to transmission cycles and maximum grant delays of theperiodic connections; and determining an awake frame candidate set ofthe wireless network device according to overlapping of the grant delayrange of each of the relaying frames, and allowing the wireless networkdevice to transmit data within the relaying frames in the awake framecandidate set.
 21. The method as claimed in claim 20 further comprising:delaying data transmission of each of the connections according to themaximum grant delay of the connection, and restricting the delayed timeof the data transmission to be less than or equal to the maximum grantdelay of the connection.
 22. A method for dynamically adjusting thesleep/awake intervals of a wireless network device, comprising:obtaining a minimum value of maximum grant delays of a plurality ofnon-periodic connections of the wireless network device according toinformation of the maximum grant delays of the non-periodic connections;obtaining a queue size according to a length of an i^(th) sleepinterval, a length of an i^(th) awake interval, and data generationrates of the non-periodic connections of the wireless network device,wherein i is a positive integer; obtaining a length of an (i+1)^(th)awake interval of the wireless network device according to the queuesize and a link capacity of the wireless network device; obtaining alength of an (i+1)^(th) sleep interval of the wireless network deviceaccording to the minimum value, the length of the i^(th) sleep interval,the length of the i^(th) awake interval, and the length of the(i+1)^(th) awake interval, and restricting a total length of the i^(th)sleep interval, the i^(th) awake interval, the (i+1)^(th) sleepinterval, and the (i+1)^(th) awake interval to be less than or equal tothe minimum value; and controlling the wireless network device to be ina sleep mode during the i^(th) sleep interval and the (i+1)^(th) sleepinterval and transmit data during the i^(th) awake interval and the(i+1)^(th) awake interval.
 23. The method as claimed in claim 22 furthercomprising: obtaining a second queue size according to the length of the(i+1)^(th) sleep interval, the length of the (i+1)^(th) awake interval,and the data generation rates of the non-periodic connections; andobtaining a length of an (i+2)^(th) awake interval of the wirelessnetwork device according to the second queue size and the link capacity,and restricting a total length of the (i+1)^(th) sleep interval, the(i+1)^(th) awake interval, and the (i+2)^(th) awake interval to be lessthan or equal to the minimum value.